The present invention relates generally to apparatus for providing a measure of the distance between the apparatus and an object. In particular, the present invention is directed to an automatic focus system in which a primary optical means, such as the taking lens of a camera, is moved to maintain an image of the object in focus at the plane of the photographic film.
One highly advantageous type of automatic focus apparatus is the spatial image correlation type. Examples of the different forms of arrangements of this type can be found in copending U.S. patent application Ser. No. 700,963, filed June 29, 1976, by Norman L. Stauffer, and assigned to the same assignee as the present invention; in U.S. Pat. Nos. 3,836,772; 3,838,275; 3,958,117; and 4,002,899, by Norman L. Stauffer, and in U.S. Pat. No. 3,274,914 by K. Biedermann, et al.
In my copending application Ser. No. 743,189, filed Nov. 19, 1976, now U.S. Pat. No. 4,078,172 issued Mar. 7, 1978 and assigned to the assignee of the present invention, I provide a continuous automatic focus system that produces an operation that occurs only with respect to the position of the major extremum to supply an accurate focus correction signal and to drive the lens in an appropriate direction to achieve proper focus. In my copending application Ser. No. 804,111, filed June 6, 1977, I provide an improved continuous automatic focus system which permits proportional control, that is, driving of the motor to position the lens at relatively high rates for large errors and reducing the speed of the motor at small errors to prevent overshoot and focus oscillation. In my copending application, Ser. No. 834,760 filed on even date herewith, I provide a further improved continuous focus proportional controller which allows the lens drive motor to operate during both the scan and return portions of the cycle and even continuously for large focus errors and which provides a small minimum drive pulse near the zero focus error, thus overcoming the static friction in the lens drive. The system also provides for characterization of the scan cycle so that the scanning mirror may actively scan the field of view during a larger portion of the cycle than was possible in the previous systems and provides means overcoming the problems associated with switch contact bounce so that only the initial closure of mechanical switches involved in the system operate to produce the control effects desired.